Metal fasteners as opposed to fasteners made of other materials, such as thermoplastic, are characterized by the possession of many desirable properties such as: high tensile strength, high and low temperature resistence, abrasion resistence, corrosion resistence and radiation resistence.
For example, one application in which metal fasteners are desirable if not essential is in the construction of high temperature insulation sheaths. A high temperature insulation sheath is constructed by enclosing a high temperature steam pipe within a sheath of insulating material, such as calcium silicate, and applying fasteners along the length of the high temperature insulation sheath to fix the insulation sheath in position. The calcium silicate insulating material is fragile and must be positioned and secured in a careful manner. In view of the fragile nature of the insulation it is desirable that the installation force necessary to install a fastener be minimized, particularly in the radially inward direction.
Different types of metal fasteners have been proposed. One type utilizes a tool to crimp and lock a metal seal onto overlapping metal straps. Reference may be made to U.S. Pat. No. 2,199,744.
In another fastener, a seal is provided with a reduced thickness central section which is inwardly deformable by a punching operation to interlock with the underlying band. Reference may be made to U.S. Pat. No. 3,754,303.
In several proposed fasteners, seals are provided which have anchoring members disposed perpendicular to the length of the strapping material. The strapping material is affixed to the seals by folding each end of the strapping material around a respective anchoring member. The first end of the strapping material is folded around a first anchoring member so that its end is disposed inwardly of the strapping material, whereby the act of tensioning the strap tends to hold the first end in place. The free end of the strapping material is drawn under and around a second anchoring member, folded over, and then secured beneath two opposing lugs with the distal edge of the strapping material projecting past the lugs. It should be understood that it is undesirable for the sharp distal edge of the strapping material to project past the lugs where it poses a safety hazard.
The lugs of the above fasteners are positioned on opposing sides of the strapping material so that when deformed over the strapping material, their longitudinal axes are perpendicular to the longitudinal axis of the strapping material. In order to deform the lugs, it is necessary to apply a significant amount of inward radially directed force, which is typically applied by repeatedly striking each lug of the fastener with a hammer. In situations where the object to be fastened is not fragile, impact force must be carefully applied to each lug to obtain a correctly deformed lug and in situations where the object to be secured is fragile even carefully applied force can damage the underlying fragile material. Examples of seals having impact deformable lugs disposed laterally of the strapping material are disclosed in U.S. Pat. Nos. 1,855,007; 2,377,224; and 2,882,934.